Consider that you can do this as a working day because someone else is plowing the fields that grow your food, probably burning stored energy in fuels for the process

We're sadly not that efficient. The 150kcal/6h=600kcal/day you've mentioned aren't enough, and it takes more than 600kcal to create 600kcal plus transportation into your home

Besides, we won't stop existing, so any math about "chatgpt uses X kW and so it's better than hiring another human" doesn't work out. The human doesn't stop burning fuels when not in use: any LLM usage is additional energy that needs to be generated while staying within CO2 budgets